- var_dump: documentation ( source)
<?php
$n = '2017-2-1';
$start = \DateTime::createFromFormat('Y-m-d', $n);
$end = new \DateTime($n . ' 1 month - 1 second');
$b = new \DateTime('2017-1-12');
var_dump($start->format('Y.M.d'));
var_dump($end->format('Y.M.d'));
var_dump($end->diff($b));